Web product with isotropic fiber orientation

ABSTRACT

Methods and apparatus to enhance paper and board forming qualities with insert tubes and/or a diffuser block in the paper forming machine headbox component which generates vorticity in the machine direction (MD) which is superimposed on the streamwise flow to generate a swirling or helical flow through the tubes of the diffuser block. Tubes of the diffuser block are designed such that the direction of the swirl or fluid rotation of the paper fiber stock may be controlled and the direction thereof is controlled in such a way to provide effective mixing, coalescence and merging of the jets of fluid emanating from the tubes into the converging section, i.e., nozzle chamber of the headbox. A specific flow inside the headbox distributes the fibers in an isotropic form, i.e., uniform in all directions, in the sheet substantially eliminating the MD preferential fiber orientation to produce an isotropic and uniform sheet. Also disclosed is the effective mixing of the jets generating cross-machine direction (CD) shear between the rows of jets that form at the outlet of the tubes inside the nozzle chamber of the headbox to align paper fibers in the cross-machine direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part of prior application Ser. No.09/645,829, filed Aug. 25, 2000, which is a divisional of priorapplication Ser. No. 09/534,690, filed Mar. 24, 2000, which is acontinuation of prior application Ser. No. 09/212,199, filed Dec. 15,1998, now abandoned, which is a continuation of prior application Ser.No. 08/920,415, filed Aug. 29, 1997, now U.S. Pat. No. 5,876,564, whichis a continuation-in-part of prior application Ser. No. 08/546,548,filed Oct. 20, 1995, now U.S. Pat. No. 5,792,321, which is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The inventions relate generally to paper forming machine headboxtube section designs and methods to improve paper properties forincreased productivity and formation quality with headbox componentshaving hydrodynamic optimization for paper and board forming. Moreparticularly, the inventions relate to the generation of a specific flowinside the headbox which distributes the fibers in an isotropic form(i.e., uniform in all directions) in the sheet eliminating “preferentialfiber orientation” and producing a truly isotropic and uniform sheet, avery desirable condition which has long been sought by papermakers.Enhanced mixing of the stock is thus provided as jets of paper fiberstock emanate from a diffuser block for coupling a distributor to anozzle chamber in a paper forming machine headbox for discharging a webproduct with isotropic fiber orientation.

[0004] 2. Background and Description of Related Art

[0005] The quality of paper and the board forming, in manufacture,depends significantly upon the uniformity of the rectangular jetgenerated by a paper forming machine headbox component for dischargingpaper fiber stock upon the wire component of the paper forming machine.The fiber orientation in current commercial paper machines isanisotropic with preference to fibers that are oriented generally in themachine direction. Attempts to establish uniform paper stock flow in theheadbox component, particularly the nozzle chamber, and to improve paperfiber orientation at the slice output of the headbox have involved usinga diffuser installed between the headbox distributor (inlet) and theheadbox nozzle chamber (outlet). The diffuser block enhances the supplyof a uniform flow of paper stock across the width of the headbox in themachine direction (MD). Such a diffuser box typically includes multipleconduits or tubular elements between the distributor and the nozzlechamber which may include step widening or abrupt opening changes tocreate turbulent flows for deflocculation or disintegration of the paperfiber stock to ensure better consistency of the stock. High qualitytypically means good formation, uniform basis weight profiles, uniformsheet structure and high sheet strength properties. These parameters areaffected to various degrees by paper fiber distributions, fiberorientations, fiber density and the distributions of fines and fillers.Optimum fiber orientations in the XY plane of the paper and board webswhich influences MD/CD elastic stiffness ratios across the width is ofsignificant importance in converting operations and end uses for certainpaper grades.

[0006] Conventional paper forming apparatus used primarily in the paperand board industry consists of a unit which is used to transform paperfiber stock, a dilute pulp slurry (i.e., fiber suspended in water atabout 0.5 to 1 percent by weight) into a rectangular jet and to deliverthis jet on top of a moving screen (referred to as wire in the paperindustry). The liquid drains or is sucked under pressure through thescreen as it moves forward leaving a mat of web fiber (e.g., about 5 to7 percent concentration by weight). The wet mat of fiber is transferredonto a rotating roll, referred to as a couch roll, transporting the matinto the press section for additional dewatering and drying processes.

[0007] The device which forms the rectangular jet is referred to as aheadbox. These devices are anywhere from 1 to 9 meters wide depending onthe width of the paper machine. There are different types of headboxesused in the industry. However, there are some features that are commonamong all of these devices. The pulp slurry (referred to as stock) istransferred through a pipe into a tapered section, the manifold, wherethe flow is almost uniformly distributed through the width of the box.The pipe enters the manifold from the side and therefore, there must bea mechanism to redirect the flow in the machine direction. This is doneby a series of circular tubes which are placed in front of the manifoldbefore the converging zone or nozzle chamber of the headbox. Thissection is referred to as the tube bundle, the tube bank or the diffuserblock of the headbox. These tubes are either aligned on top of eachother or are placed in a staggered pattern. There are anywhere from afew hundred to several thousand tubes in a headbox.

[0008] The tubes in current headboxes have a smooth surface startingfrom a circular shape in the manifold side and going through one or twostep changes to larger diameter circular sections. Some tubes convergeinto a rectangular outlet (some with rounded edges) at the other endopening to the converging zone of the headbox. Analysis shows that theflow entering the tube may start to recirculate generating vorticity inthe machine direction. The sign of the vorticity vector depends on thelocation of the tube. Very often, there is a pattern that develops as anatural outcome of the tube pattern structure and the structure of theheadbox. In current machines, there is no control on the direction orstrength of the vortices in the tubes. The tubes all have flat smoothinternal surface and the flow pattern and secondary flow inside thetubes is governed by the inlet and outlet conditions. The machinedirection vorticity could be positive or negative depending on the inletand outlet conditions which in turn depend on the location of the tubein the tube bank.

SUMMARY OF THE INVENTION

[0009] The present invention relates to the control and formation ofsecondary flow in the tubes in order to achieve a superior flow fieldinside the converging zone of the headbox to achieve certain flowproperties in the converging zone of the headbox. Thus, the conceptrelates to the modification of the flow inside the tube bank by alteringthe internal surface geometry of current tubes or tube inserts. Theinternal surfaces of all of the current tubes or tube inserts are eithercircular and therefore axisymmetric (type I), or, they start from acircular inlet and eventually converge into a rectangular outlet (typeII) with a four fold symmetry (i.e., the entire tube can be divided intosymmetric regions by two diagonal cross-sectional planes, one verticalcross-sectional plane and one horizontal cross-sectional plane. The newconcept is to modify the geometry of the type I and/or inserts such thatthe internal surface is no longer axisymmetric or non-axisymmetric, andto modify the internal geometry of the type II tubes such that theinternal geometry of the tube or the insert is no longer four foldsymmetric. One described embodiment modifies the internal geometry ofeach tube in order to generate machine-direction (MD) vorticity andsubsequently to arrange the tube or the insert in such a manner so thatall the jets in each row of the tube bundle form with the same sign ofMD vorticity vector and the jets in each column form with alternatingsign of the MD vorticity. This generates shear layers which would resultin cross-machine orientation of fibers and therefore would increase thestrength and other physical properties in the CD while providingeffective mixing and turbulent generation between tubes adjacent to eachother in each row.

[0010] Another described embodiment modifies the internal geometry ofeach tube insert or tube in order to generate machine-direction (MD)vorticity and subsequently to arrange the tubes or the inserts in such amanner so that all the jets in each row and column of the tube bundleform with the same sign of MD vorticity vector. This results in strongmixing and dispersion of the fibers and fillers and therefore betteruniformity in fiber and filler distribution in the sheet.

[0011] Another mechanism to generate axial vorticity inside the tubes ofa headbox is to have a device, a tube insert, wherein a flat section atthe manifold side is followed by a converging curved section, followedby a straight tube section, and where, one or more inclined fins orgrooves are placed on the flat section or on the flat and the convergingcurved section of the headbox tube or insert nozzle of the headbox tube.The purpose of inclined fins or grooves is to control the defineddirection or orientation of the axial vortices generated inside thetubes. The converging section of the insert nozzle or tube willaccelerate the fluid and increase the angular velocity of the fluid,consequently, increasing the strength of the vortex as the fluid movestoward the straight (constant diameter) section of the tube. In anotheralternate embodiment, the generation one or more counter-rotating vortexpairs (CVPs) may be set up inside each tube instead of a single vortexper tube.

[0012] Briefly, the invention relates to methods and apparatus toenhance paper and board forming qualities with insert tubes and/or adiffuser block in the paper forming machine headbox component whichgenerates vorticity in the machine direction (MD) which is superimposedon the streamwise flow to generate a swirling or helical flow throughthe tubes of the diffuser block. Tubes of the diffuser block aredesigned such that the web product with isotropic fiber orientation ofthe paper fiber stock may, be controlled by generating controlled axialvortices promoting mixing of the jets of paper stock from the tubularelements as the jets flow into the nozzle chamber to a uniform flowfield of stock at the slice opening for the rectangular jet. Alsodisclosed is the effective mixing of the jets generating cross-machinedirection (CD) shear between the rows of jets that form at the outlet ofthe tubes inside the nozzle chamber of the headbox to align paper fibersin the cross-machine direction.

[0013] The appended claims set forth the features of the presentinvention with particularity. The invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1A shows a paper forming machine headbox component used witha diffuser block exposed to show vortex forming means provided for aplurality of the tubular elements of the diffuser block in accordancewith the invention;

[0015]FIG. 1B shows a cross-sectional view thereof;

[0016]FIG. 1C shows an insert tube embodying vortex forming means alsoin accordance with the invention for insertion in the diffuser block ofa conventional paper forming machine headbox component;

[0017]FIG. 1D illustrates a tubular element of a step diffuser block forgenerating controlled axial vortices therein;

[0018]FIGS. 2A and 2B show an additional embodiment of the inventionwherein fins or grooves at the inlet of the tubular element may beutilized to generate vortices and converging section can curved sectionforming an elongated portion near the inlet also generate controlledaxial vortices within tubular elements;

[0019] FIGS. 3A through FIG. 3H illustrate various controlled vorticesconfigurations as positive and negative defined vortices emanating fromthe diffuser block to generate small scale turbulence between adjacenttubes for improved formation, and predetermined cross flows to achieveuniform stock flow in the nozzle chamber according to the invention;

[0020] FIGS. 4A-4H illustrate stock flow irregularity associated withconventional paper forming machine headbox components;

[0021] FIGS. 5A-5H illustrate the use of controlled axial vortices inthe paper stock jets to provide more uniform paper stock flows in thenozzle chamber approaching the slice of the paper forming machineheadbox component in accordance with the invention.

[0022]FIG. 6 is a side view cross-section of a tube in the tube bank ofthe headbox;

[0023]FIGS. 7A and 7B show the location of pressure pulse generators inone embodiment of the invention;

[0024]FIG. 8 is a cross-section view of a tube showing mounting detailsof an acoustic pressure pulse generator;

[0025]FIG. 9 is a cross-section view of a tube showing mounting detailsof a magnetically actuated finned body for generating vortexes;

[0026]FIG. 10 is a side view and front view of the finned body shown inFIG. 9;

[0027]FIG. 11 shows a pair of counter-rotating vortices delivered fromeach tube in the block in an XY±pattern;

[0028]FIG. 12 shows a pair of counter-rotating vortices delivered fromeach tube in the block in an XX±pattern;

[0029]FIG. 13 shows a pair of counter-rotating vortices delivered fromeach tube in the block in an XX₊ ⁺ pattern;

[0030]FIG. 14 shows a pair of counter-rotating vortices delivered fromeach tube in the block in an XY₊ ⁺ pattern;

[0031]FIG. 15 shows the delta shaped block placed at the exit section ofthe small diameter tube;

[0032]FIG. 16 shows the delta shaped block placed at the mid-section ofthe large diameter tube;

[0033]FIG. 17 shows the jet of Fluid B impinging on the Fluid A jetleaving the small diameter tube resulting in jet breakup into a CVP;

[0034]FIG. 18 shows the jet of Fluid B impinging on the Fluid Amainstream flow in the larger diameter tube resulting in a CVP;

[0035]FIG. 19 shows two pairs of counter-rotating vortices in each tubearranged in XX pattern, the two small squares inside the tubesrepresenting the general location of the protuberance;

[0036]FIG. 20 shows two pairs of counter-rotating vortices in each tubearranged in XY pattern, the two small squares inside the tubesrepresenting the general location of the protuberance;

[0037]FIG. 21 is a perspective view of a small diameter tube design inaccordance with the invention;

[0038]FIG. 22 is an end view of the tube showing the closed core andtube fins of the tube of FIG. 21;

[0039]FIG. 23 is a sectional view of the tube of FIG. 21 taken as across section from FIG. 22;

[0040]FIG. 24 is a plot of the mesh;

[0041]FIG. 25 shows velocity vectors on the center plane for the entiremodel;

[0042]FIG. 26 shows axial velocity contours on the center plane for theentire model;

[0043]FIG. 27 shows velocity vectors on the center plane for the finsection only;

[0044]FIG. 28 shows axial velocity contours on the center plane for thefin section only;

[0045]FIG. 29A is an Excel plot showing axial velocity plotted atvarying angles 5 mm past the end of the fins;

[0046]FIG. 29B shows the same at one diameter past the fins;

[0047]FIG. 30A shows the components of swirl taken along a line 45degrees to the coordinate axes 5 mm past the end of the fins; and

[0048]FIG. 30B shows the above one diameter past the end of the fins;

[0049]FIG. 31 is a polar diagram illustrating the anisotropic fiberorientation illustrates fiber orientation with a preference to themachine direction;

[0050]FIG. 32 illustrates the reorientation of paper fibers providingisotropic fiber orientation for discharge as a web product resulting inhigher cross-machine direction (CD) strength providing fiber orientationsubstantially equally in all in-plane directions as shown in the polardiagram;

[0051] FIGS. 33A-33C illustrate various manifestations of fiberorientation nonuniformity showing anisotropic paper having preferentialfiber orientation which is typically distributed relative to the machinedirection as shown in the polar plots, whereas FIG. 33D illustrates auniform isotropic orientation; and

[0052]FIG. 34 shows a polar diagram of in-plane elastic content showingthe orientation distribution of the strength of the web product forpilot trial samples of linerboard produced in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0053] Reference will now be made in detail to the present preferredembodiments, examples of which are illustrated in the accompanyingdrawings. FIG. 1A illustrates an embodiment of a paper forming machineheadbox component 10 for receiving a paper fiber stock and generating arectangular jet therefrom for discharge upon a wire component moving ina machine direction (MD). A distributor 12 is provided for distributingthe paper fiber stock flowing into the headbox component 10 in across-machine direction (CD) which would be generally perpendicular tothe machine direction of the wire component in a conventional hydraulicheadbox. It is important to note however, that the present invention mayalso be embodied in a conventional air-cushioned headbox as well as thehydraulic headbox. The distributor 12 is provided to supply a flow ofpaper fiber stock across the width of the headbox 10 in the machinedirection. A nozzle chamber 14 is shown having an upper surface and alower surface converging to form a rectangular output lip defining aslice 22 opening for the rectangular jet at opening 24. As shown incross section in FIG. 1B, the paper fiber stock flows as indicated bythe arrows in the nozzle chamber 14 to output the rectangular jet 30upon the wire 32 partially shown in FIG. 1B.

[0054] A diffuser block 16 is provided to couple the distributor 12 tothe nozzle chamber 14. As illustrated in FIGS. 1A and 1B, the diffuserblock 16 includes a multiplicity of individual tubular elements 18disposed between the distributor 12 and the nozzle chamber 14, thepresently described embodiment includes vortex forming means 20 providedfor a plurality of the tubular elements 18. The vortex forming means 20embodied herein may be provided for a subset or a plurality of themultiple tubular elements 18 for generating controlled axial vortices inthe machine direction promoting mixing of the jets of the stock from thetubular elements 18, as the jets flow into the nozzle chamber to auniform flow field of stock at the slice opening 22 for the rectangularjet 30 from the rectangular opening 24 at the slice 22.

[0055] As FIG. 1B illustrates in cross section, steps 26 and 28 as mightbe found in a conventional diffuser block for the purpose of breaking updeflocculation or disintegrating the paper fiber stock to enhance theuniformity thereof. As already described a step diffuser block isgenerally provided in conventional headboxes, and the present embodimentmay or may not require the use of such a step diffuser, but for thepurpose of the described embodiment, the step diffuser is provided asshown.

[0056]FIG. 1C shows an insert tube 34 which is insertable in a diffuserblock for coupling the distributor to the nozzle chamber in a paperforming machine headbox for discharging paper fiber stock upon a wirecomponent moving in a machine direction. The diffuser block inconventional machines includes a multiplicity of individual tubularelements as already discussed and also provide for the ability for suchinserts, typically smooth cylindrical tubular inserts for varyingdiameter of the individual tubular elements. However, the inserts of thedescribed embodiment and shown herein are typically used to generatevortices within such tubes and thus, asymmetric or non-axisymmetricsurface with ridges or fins or grooves as opposed to smooth axisymmetricinner surfaces are employed. The tubular elements and the insert tubesare oriented axially in the machine direction and arranged as a matrixof rows and columns for generating multiple jets of paper fiber stockflowing into the nozzle chamber 14. The insert tube 34 includes a flatsection inlet 36 for receiving the stock from the distributor, whichalso serves as a shoulder or rim for securing the insert tube 34 in thediffuser block 16. The insert tube 34 embodiment also includes anelongated section outlet 38 connected to the flat section inlet 36 fordirecting the jets of the paper fiber stock through the tubular elementsof the diffuser block 16 as the jets flow towards the nozzle chamber 14.Also the vortex forming means 40 are provided for the insert tube 34 forgenerating the controlled axial vortices in the machine direction topromote mixing of the jets from the elongated section outlet as the jetsflow toward the nozzle chamber 14. Herein, the vortex forming meansinclude an asymmetric interior surface as shown in FIG. 1C within theelongated section outlet 38 for generating the controlled axial vortextherein. More specifically, the asymmetric interior surface has a spiralpitch defining a helical path as shown within the tubular elements togenerate the controlled axial vortices as the stock travels along thehelical path in the elongated section outlet 38. Thus, as described, fortubes in existing headboxes, the insert tube 34 may be constructed ofplastic, metal, ceramic or composite inserts with the spiral-shapedgrooves, fins, ridges or guides of various form at the inner surface.One such feature is to form spiral-shaped grooves or patterns throughthe inner surface of the insert as shown. These inserts can be easilyplaced inside the tubes to generate the desired machine-directionvorticity in the tube. The inserts such as tube insert 34 may be placedinside the tubes at the distributor or manifold side of a headbox 10.The initial section of the insert at the inlet may start with a smoothsurface before the vortex generating means, discussed above.

[0057] Turning now to FIG. 1D, there are several ways to implement thedescribed concept, e.g., the tubes have the feature of directing theflow in a manner to generate machine direction vorticity in a specificdirection (i.e., with a specific vorticity vector sign, defined aspositive (+) or negative (−) based on a right-hand rule). Thus, the signof the secondary flow of the vorticity inside the tube is controlled bythe spiral-shaped grooves, fins, ridges or guides of various form in theinner surface or such means for generating the vorticity. One suchfeature is to form spiral-shaped grooves or patterns through the innersurfaces of the tubes as shown in FIG. 1D, in a step diffuser box. Asthe fluid enters the tube from the manifold, the spiral grooves directthe flow in a recirculating manner generating or increasing thecontrolled vorticity in the machine direction. The grooves haveincreasing or decreasing pitch depending on the type of tube and theheadbox design. As shown in FIG. 1D, the pitch of the spiral-shapedgrooves may gradually change through the step diffuser tube as indicatedby reference numerals 42, 44 and 46; note particularly the increasedpitch between the groove 44 and the groove 46. The pitch of the groovesdepends on the average MD velocity through the tube. If the MD velocityis very large, then the pitch may be considerably smaller than shown inthe figure. Another means to generating the controlled vortices inaddition or in place of the spiral grooves or fins, discrete sections offins or ridges can be used to direct the stock in a helical patterninside the tubes generating controlled MD vortices. The spiral-shapedgrooves, fins or guides allow the fluid to gradually flow in thespiral-shaped pattern of the tube surface.

[0058] With reference to FIGS. 2A and 2B, additional tube insertembodiments are shown including vortex forming means as an inclined finor groove 56 and 70 on flat section inlets 48 and 62 respectively. Suchincline fins or grooves facilitate the generation of the controlledaxial vorticity as the stock flows toward the elongated section outletfrom the distributor 12 of the headbox 10. The mechanism of FIGS. 2A and2B generate axial vorticity inside the tubes of the headbox wherein theflat section at the manifold or distributor side is followed by aconverging curved section, herein curved sections 50 and 64 andconverging portions 52 and 66 are provided as portions of the elongatedsection outlet connecting to elongated sections 54 and 68 respectively,in the two embodiments of FIGS. 2A and 2B. Where the inclined fin orgroove, e.g., 56 or 70, is placed on the flat section, e.g., 48 or 62,or on the flat and the converging section of the headbox tube or insertnozzle of the headbox tube, the purpose of the inclined fin or groove isto control the direction of the vortex generated inside the tube asshown wherein inlet flow 58 is directed as a vortical flow patternindicated by reference numeral 60 in FIG. 2A; and incoming flow 72 isdirected as vortical flow 74 in the embodiment of FIG. 2B. Theconverging sections 52 or 66 of the insert tube will accelerate thefluid and increase the angular vorticity of the fluid, consequentlyincreasing the strength of the vortex as the fluid flows towards thestraight edge 54, or 68 of the tube. FIG. 2 shows the groove 56 asresiding within the elongated outlet portion of the tube as well as onthe flat section 48; while FIG. 2B provides the groove or fin 70 asresiding solely on the flat surface 62. It should be noted that while asingle fin or groove is shown on the tubes more fins may be desirablefor creating the axial vorticity within the tubes as well as for ease ofplacement, orientation independence and the like for fitting such tubesinto the diffuser block of conventional headboxes. The curved sections50 and 64 may be incorporated into the elongated section and disposedbetween the flat section 48 and converging section 52 in FIG. 2A tofacilitate the axial vorticity, and as such, provide additional vortexforming means as a curved section included along a portion of theconverging section near the flat section for generating the controlledaxial vortices as the paper fiber stock flows in the elongated sectionoutlet.

[0059]FIGS. 3A, 3B and 3C illustrate various methods of mixing jets ofpaper fiber stock emanating from a multiplicity of axially aligned tubesarranged as a matrix of rows and columns in a diffuser block coupled toa nozzle chamber in a paper forming machine headbox for discharging auniform flow field of stock upon the wire component moving in themachine direction. As indicated, the MD components of vortices of thejets emanating from the tubes are indicated as positive defined ornegative defined axial vortices in accordance with the convention of theright-hand rule and where here we use the convention that positive MDpoints into the surface of the figures. One could also use theconvention that MD is the negative direction. Positive or negative. jetsrefer to jets with positive or negative MD vorticity, respectively. Amethod described herein provides for the generation of positive jets ofpaper fiber stock emanating from the diffuser block in controlled axialvortices in the machine direction for a first plurality of the tubes,the direction of the vortex being directed in a first positive-defineddirection about the axes of each of the first plurality of tubes andpositioning at least one of the positive jets adjacent another one ofthe positive jets promoting mixing as the jets flow into the nozzlechamber. This is illustrated in FIG. 3A where the first row 76 of FIG.3A and the bottom row 80 of FIG. 3A whereby small scale turbulence isintroduced between the individual positively oriented jets of rows 76and 80 as the fluid flow emanates from the tubes promoting mixingthereof. Small scale turbulence is also introduced between theindividual negatively oriented jets of row 78 in FIG. 3A. In addition tothe secondary vorticity of the jets promoting mixing of the fluidemanating from the tubes, the configuration of FIG. 3A also generatesshear layers which would result in cross-machine orientation of fibersand therefore, would increase the strength and other physical propertiesin the cross-machine direction, as indicated by shear layers in between82 and 84 with the inner-posed layer of negative defined rows ofvorticity as indicated by reference numeral 78. The jet orientation ofrow 78 is provided according to the method by generating negative jetsof paper fiber stock emanating from the diffuser block in controlledaxial vortices in the machine direction for a second plurality of tubes,the direction of each vortex being directed in a second negative-defineddirection about the axes of each of said second plurality of tubes andpositioning at least one of the negative jets adjacent another one ofthe negative jets promoting mixing as the jets flow into the nozzlechamber, herein row 78. FIG. 3A illustrates desired flows for enhancingthe strength of paper or board because the shear layers in the CDprovide CD strength by the alternating MD vorticity direction of thesecondary flow of the jets from the tubes in each row of tubes resultingin shear layers which align more fibers in CD.

[0060] An alternate concept of modifying the internal geometry of eachtube in order to generate machine direction vorticity and subsequentlyarrange the tubes or inserts in a manner such that all the jets of eachrow and column of the tube bundle form the same sign of MD vorticityvector is shown in FIG. 3B. This results in strong mixing and dispersionof the fibers and fillers and therefore better uniformity in fiber andfiller distribution in the sheet and enhanced formation. As shown inFIG. 3B all of the rows and columns have the orientation same indicatedby reference numeral 86, namely a positively defined orientation ofvorticity which results in turbulent shears as indicated by referencenumeral 88 and 90. FIG. 3B shows an orientation best for mixing whereuniform dispersion is a criteria having emphasis over strength; such asin tissue or light-weight paper applications.

[0061]FIG. 3C illustrates alternating sign vorticity 92 and 94throughout the rows and columns of the tube bank which provides theconfiguration of Case 2 discussed below in connection with FIGS. 5A-5Hwherein the described counter-rotating pattern of adjacent jets providesbetter mixing over jets lacking vorticity discussed further below.Computer analysis for headboxes employing the configuration of FIG. 3Cshows the ability to achieve more uniform flow of the paper fiber stockwithin the nozzle chamber making secondary jets at the slice weaker andthus noticeable improvement in uniformity.

[0062]FIGS. 3D, 3E and 3F show additional patterns of the tubes forgenerating vortices of defined orientation, herein the matrix of rowsand columns in the diffuser block being either vertical or inclinedcolumns and introducing the vortex patterns in staggered tubearrangements. FIGS. 3D, 3E and 3F respectively provide patterns similarto those discussed above in connection with FIGS. 3A, 3B and 3C, whereinthe individual secondary vorticity of the jets emanating from the tubesis provided in a staggered pattern in FIGS. 3D-3F. In FIG. 3D, thealternating MD vorticity direction of the secondary flow of the jetsfrom the staggered tubes results in shear layers which would align morefibers in the CD. In FIG. 3E, the MD vorticity direction of thesecondary flow of the jets from the staggered tubes results in enhancedfiber dispersion and mixing of the fillers in the paper fiber stock. InFIG. 3F, the alternating checkerboard MD vorticity direction of thesecondary flow of the jets from the staggered tubes results in effectivemixing and fiber dispersion.

[0063] Additionally, FIG. 3G illustrates plural row pairs of commonsecondary vorticity of the jets from the tubes in a staggered pattern,herein a pair of negatively oriented rows 96 being provided above a pairof positively oriented rows 97 in a repetitive pattern. Accordingly, thealternating MD vorticity direction of the secondary flow of the jetsfrom the staggered tubes in FIG. 3G results in shear layers which wouldalign more fibers in the CD. From the foregoing, it is appreciated tothose skilled in the art that the tubes arranged as a matrix of rows andcolumns in the diffuser block are provided either vertically or inclinedand the rows or columns may be provided as staggered for enhancing fiberalignment. FIG. 3H similarly shows a repetitive pair vorticity patternillustrating, e.g., negatively oriented rows 98 and positively orientedrows 99.

[0064] Turning now to FIGS. 4A-4H and FIGS. 5A-5H, the effect ofvorticity in the tubes of the headbox 10 on the flow is illustrated forthe slice and the nozzle chamber 14. Here, analysis shows the effect ofvorticity in the jets leaving the tubes in the tube bank and enteringthe converging zone of the headbox. The purpose of this study is toinvestigate the effect of vorticity at the tube bank on the free surfacerectangular jet 30 at the slice 22. Two cases have been considered, caseone with no vorticity and the second case with axial vorticity. Thesecases are shown in FIGS. 4A and 5A, respectively.

[0065] The tubes in these cases, i.e., case #1 (FIGS. 4A-4H) and case #2(FIGS. 5A-5H) are arranged in vertical columns, as shown in FIGS. 4A and5A, respectively. The flow through the tube in case 1 has velocitycomponent only in the machine direction. Wherein case 2, the flow in thetube has an axial vorticity imposed on the streamwise flow. The imposedsecondary flows are counter-rotating axial vortices, that is thedirection of rotation is clockwise and counter-clockwise in acheckerboard pattern. The cross machine direction, y, and the verticalz, components of the velocity at the tube outlet and the converging zoneinlet are given respectively by: $\begin{matrix}{{v = {{\pm A}\frac{2\pi}{\Delta \quad y}\cos \frac{2\pi \quad y}{\Delta \quad y}\sin \frac{2\pi \quad z}{\Delta \quad z}}}{and}} & \text{(1a)} \\{w = {{\pm A}\frac{2\pi}{\Delta \quad z}\cos \frac{2\pi \quad z}{\Delta \quad z}\sin \frac{2\pi \quad y}{\Delta \quad y}}} & \text{(1b)}\end{matrix}$

[0066] These velocity components are super-imposed on the streamwisevelocity component of the jet leaving the tubes as shown in FIG. 5A. Inequation (1a, 1b) w and v are the vertical (Z) and transverse (CD)components of velocity, A is the magnitude of the secondary flow at theinlet, Δy and Δz are the horizontal and vertical dimensions of the tubeoutlet, respectively. The magnitude A, of the super-imposed secondaryeddy in this study is 1.5% of the average streamwise component. Thesecondary velocity profile at the inlet to the converging zone isdefined by a 4th order function of the y and z coordinates. The Reynoldsnumber, based on the average inflow velocity U, the vertical height ofthe headbox L, and the kinematic fluid viscosity, v, is given by:$\begin{matrix}{{R\quad e} = \frac{U\quad L}{v}} & (2)\end{matrix}$

[0067] The results of the two cases are described herein with theanalysis of computational experiments. The flow characteristics at theslice for each case is given by presenting the contour plot of each ofthe three velocity components (see FIGS. 4C-4H and FIGS. 5C-5H). Sincethe direction of the secondary flows cannot be identified in the blackand white reproduction of the color-coded plots, we have added arrows tothe plots to distinguish the flow direction.

[0068] For the first case, where the tubes are arranged in a straightvertical column, the flow is periodic with a wavelength of one-third ofthe width of the computation domain. The vertical component of the flowplays an important role in transferring fluid of high streamwisemomentum towards the bottom wall of the headbox. Due to the periodicityof the flow, this momentum transfer varies significantly in the CDdirection. Where the vertical velocity towards the wall is larger, thefaster moving fluid carried from the middle of the slice to the wallforms a liquid jet. Where the vertical velocity is relatively smaller, astreamwise velocity jet of lower speed appears. These liquid jets can beseen in FIGS. 4D, 4F and 4H, where the contour plot of the threevelocity components for this case are plotted along a horizontalcross-sectional plane near the lower lip of the slice. Removing theaverage vertical velocity from the actual vertical velocity reveals thecellular pattern of the secondary flow structure. The secondary flowpatterns at the slice for each of the two cases are illustrated in thecontour plots. The contour plots of the average velocity components forcases 1 and 2 at a horizontal cross-sectional plane are shown in FIGS.4D, 4F, 4H and FIGS. 5D, 5F and 5H, respectively.

[0069] The vertical velocity component contour plot in FIGS. 4G, 4E and4C show that the flow at the slice has a periodic structure similar tothat in Case 1 (i.e., FIGS. 5G, 5E and 5C). However, in this case thedeviation of the actual vertical velocity from the average verticalvelocity is smaller. Consequently, less fluid with high streamwisemomentum is transferred towards the bottom surface of the headbox. Also,less fluid with low streamwise momentum is lifted from the lower surfacetowards the middle of the slice. Thus, the secondary jets at the slicefor Case 2, are weaker and less noticeable. Compared to Case 1, thesecondary fluid flow cells created in this case are further away fromthe bottom and the CD velocity components are smaller than those of thefirst case.

[0070] In Case 1, the vertical velocity component changes sign and thevariation in streamwise velocity due to the jets from the tubes remainstrong up to the slice. As seen from the contour plot of the z componentof velocity, there is considerable non-uniformity in the velocity. Thiskind of flow results in a streak pattern when manufacturing light-weightsheets. In the other case, however, the vertical component, as well asother components of the flow field, are more uniform due to the vorticeswhich result in more effective coalescence and mixing of the jets.

[0071] The counter-rotating pattern of adjacent jets, as considered inthis study, is perhaps not the most effective pattern for mixing of thefluid and suspended particles in jets from adjacent tubes. A moreeffective method for mixing is to force the jets from the tubes torotate in the same direction. Depending on the desired properties of thesheet, the rotational pattern of the jets should be accordinglycontrolled using the special tubes outlined above and the specificpattern arrangement of FIGS. 3A, 3B or 3C, as appropriate.

[0072] In another embodiment, the vortex swirls are induced by means ofpressure pulse generating elements. This method has three distinctadvantages:

[0073] 1) the generation of the secondary flow or swirl in the tubes canbe fine-tuned on-line as the machine is in operation without anydisturbances to the production,

[0074] 2) the swirl number or the strength of the secondary flows can beadjusted in individual rows of tubes or in individual sections of thetube bank on-line while the machine is in operation without anydisturbances to the paper machine production, and

[0075] 3) no spiral finds or grooves or other constrictions are placeinside the tubes; therefore, the probability of tube plugging is reducedbelow the conventional tubes.

[0076] Conventional tubes have two general sections. The first sectionis a small diameter tube which contacts at one end with the manifold ordistributor of the headbox. On the other end, the small diameter tubeconnects to a larger diameter tube through a step change incross-sectional area, as shown in FIG. 6.

[0077]FIG. 6 shows a side-view cross section schematic of a tube in thetube bank of the headbox and the flow pattern from the small diametertube at the left to the larger diameter tube. The doughnut shaped vortexis not axisymmetric since the jet from the small diameter tube bendsrandomly to attach to the wall of the large diameter tube. Often the jetchanges angle in a random manner.

[0078] This embodiment provides a method and device to regulate thebending characteristics of the jet from the smaller diameter tube inorder to generate a desired flow pattern at the outlet of the largerdiameter tube. The described embodiment provides of a tube with asmaller diameter section followed by a step change or a more gradualchange of diameter to a larger diameter tube—there are 2 to 12 pressurepulse generators 102 (PPG) at ports near the throat of the tube as shownin FIG. 7A. The pressure gradient pulses are generated in a given timesequence in order to control and regulate the bending of the jet fromthe smaller diameter tube. The schematic of this embodiment is shown inFIG. 7B. The device consists of several (8 ports are shown in FIG. 7B)PPG units which operate with an electric signal connected to ananalog-to-digital converter (A/D) board and a digital processor (acomputer).

[0079] The PPG can either be an acoustic device generating a pulse ofacoustic pressure in the form of longitudinal waves inside the fluid oran electromagnetic device generating a magnetohydrodynamic (MH) pulse.The purpose of the pressure gradient pulse or the MH pulse is to controland guide the bending of the jet from the smaller diameter tube. Uponactivation of a PPG, the jet can be forced to bend almostinstantaneously in the direction opposite to the propagation of thepressure gradient pulse. For example, the activation of PPG at port 7forces the jet to bend in the direction shown in that figure. If the PPGat ports 3 and 7 are activated in a time periodic manner, the jetoscillates back and forth in a time periodic manner. If PPG 1 to 8 areactivated in a sequential manner (i.e., 1, 2, 3 . . . , 8, 1, 2, . . . )the jet will rotate counter-clockwise with a slight phase lag.Activation of ports 8 to 1 will force the jet to rotate in the clockwisedirection. Rotation of the jet around the larger diameter tube resultsin a swirling jet at the outlet of the tube. The swirl number, S, can becontrolled with the frequency of activation of the PPG. Higher frequencywill result in more swirl and larger swirl number, S.

[0080] It is important to note that the flow characteristics inside thetubes can be fully controlled with the sequence and the frequency of theactivation of the PPG.

[0081] In a typical headbox, there are N tubes inside the tube bankwhere N could be several hundred to few thousand depending on the sizeof the headbox. The tubes are arranged in R number of rows, where10>R23, and C=N/R columns.

[0082] With this embodiment each tube can be independently controlled,if desired. It is also easy to control blocks of tubes; for example,each row of tubes could have independent control, as well as, eachcolumn of tubes from column 1 to q and from Column C-q to C could becontrolled, independently. The magnitude of q depends on how far fromthe side walls the tubes need to be controlled independently forsuperior control of the flow near the side wall and the edge of theheadbox and the forming section.

[0083] One form of a PPG consists of a small flat plate, up to a fewmillimeters in diameter and less than a millimeter thick, which is flushwith the inner surface of the tube. The surface would oscillategenerating longitudinal pressure gradient waves with the application ofelectric field to a piezoelectric crystal adjacent to it. The vibrationof the surface generates an acoustic field which propagates into thefluid generating a longitudinal wave. The setup of the PPG in the portat the throat of the tube is illustrated in FIG. 8. Another PPG elementmay be provided in the form of a ring which is positioned flush with theinterior surface of the curved outlet of the insert of the smallerdiameter section of the tube. The ring-shaped PPG is activated locallyin a circular manner. The angular location of activation generated apressure disturbance which deflects the jet, as shown in the diagram, toone side. Continuous activation of the PPG element in a circular mannerwill force the jet to rotate around the curved surface of the insertgenerating a swirling motion of the fluid inside the larger diametertube.

[0084] A further mechanism to generate swirl inside the tubes in thetube bank of a headbox is by the use of magnetic force where anon-axisymmetric body of revolution 101 is placed inside an axisymmetrictube 103, as shown in FIG. 9. The metallic body of revolution 101consists of an axisymmetric central region 105 shown in FIG. 10 and oneto twelve fins. The most practical system would have three (F-3) to four(F-4) fins, as shown in FIG. 10. The fins could be straight or spiralshaped. The central body of revolution, 101, is partially hollow andconsists of metallic sections or poles. The overall float is designed toexperience up to three components of magnetic force, F1, F2 and F3 andone component of torque, T1, from the magnetic rings 109, 111 and 113.Two of the three components of force consist of axial forces in oppositedirection from magnetic rings 109 and 111. The third component of forceis a radial magnetic force from the electromagnetic ring 113, whichholds the “float” in the center of the 117 section of the tube. Theelectromagnetic ring 113 also exerts a torque, T, on the “float”. Thetwo opposing axial forces and the radial force from electromagnetic ring113 hold the “float” in the center of the tube section 115. The torquefrom the electromagnetic ring 113 forces the “float” to rotate at aspecific rate of rotation. The torque from the electromagnetic ring isvariable according to the power supplied to the magnetic coil.

[0085] There are also hydrodynamic forces on the “float” duringoperation which resist the motion of the “float”. The hydrodynamicforces are the normal stress (force per unit area normal to the surfaceof the “float”) and the tangential stress (shear stress at the surfaceor drag per unit surface area). The magnetic forces and torque areadjusted considering the hydro-dynamic forces to keep the “float” at thecenter with the float rotating at a specific rate of rotation (usuallybetween 5 to 100 cycles per second or Hz).

[0086] The rotation of the “float” inside section 117 generates aswirling flow inside the tube which persists into section 110 andfurther downstream through the outlet of the tube into the convergingzone of the headbox. The amount of swirl can be adjusted by the amountof torque exerted on the “float”0 by electromagnetic ring 113. Thefaster the rate of rotation of the “float”, the higher the swirl numberinside the tube. The magnetic strength of the electromagnetic ring 113can be adjusted on-line during operation to control the amount of swirlin individual tubes. Therefore, this method allows a fully automaticmethod to easily control the amount of swirl in individual tubes duringoperation attaching the electromagnetic ring 113, of each of the tubesto an electronic control system. An alternate mechanism may employ finsextended from the solid ring as a “rotor”, which fits inside the tube.The ring is forced to rotate at a controlled angular speed by a magneticfield, such as the electromagnetic ring or other means. The same effectof generating a swirling flow inside the tube is obtained with thisdevice.

[0087] In another alternate embodiment, the generation one or morecounter-rotating vortex pairs (CVPs) may be set up inside each tubeinstead of a single vortex per tube. The counter-rotating vorticesinside the tubes result in more effective interaction of the jets onceleaving the tubes. The CVPs may be generated in four orientations in thetube block, as demonstrated in FIGS. 11 through 14. Only the secondaryflow pattern, that is the flow in the cross-sectional plane of the tubesis shown in these figures. These figures show three rows and threecolumns of the tubes in the tube block. As shown in these figures, themanner by which the secondary flows in the jet interact depend on thesecondary flow pattern formed in the collection of tubes in the tubeblock.

[0088] The interaction of the adjacent jets from the tubes in the tubebank result in higher level of shear and extensional flow perpendicularto the streamwise direction in the converging nozzle of the headbox.This results in a more uniform fiber orientation in the forming jetleaving the headbox. That is with the correct level of axial vorticityin the jets leaving the tubes, the interaction between the jets will besuch as to prevent fiber orientation in the streamwise direction. Thisresults in an isotropical fiber orientation at the forming jet leavingthe slice of the headbox.

[0089] When the orientation of the CVPs in each adjacent tube in a rowvaries alternatively, then the pattern is designated as an XY form.Otherwise, if the orientation of secondary flows in each tube in the rowis the same, the pattern is identified as the XX pattern. To identifythe secondary flow patterns that change alternatively in adjacent tubesin a column, the symbol ± is used; otherwise when the orientation issame in each column, the pattern is symbolized with the ₊ ⁺ notation. Bycomparing the patterns in FIGS. 11 through 14, one can see thedifference between the manner by which the secondary flows interact; inother words, the different form the adjacent jets from the tubes in thetube block interact.

[0090] To explain the form of interaction between the jets in the tubeblock, let us define a cylindrical polar coordinate system (r, θ, z), todefine the radial, azimuthal, and axial directions of flow in the tubeswith respective velocity components (U_(r),U_(θ),U₂). The primary flowis represented by the axial velocity component, u₂, where the other twocomponents in the radial and azimuthal directions are referred to as thesecondary part of the mean flow.

[0091] One mechanism to generate the CVP is based on the naturaltendency of jets to form vortices when encountering a pressure gradientin the radial and azimuthal directions. From now on, we will refer tothis variation in pressure as the Radial-Azimuthal-Pressure Variation(RAPV). Variation in pressure according to RAPV will result in CVPs withswirl number, S, defined for each vortex as$S = \frac{\int\limits_{0}^{R}{r^{2}u\quad w{r}}}{R{\int\limits_{0}^{R}{{r\left( {u^{2} - {\frac{1}{2}w^{2}}} \right)}{r}}}}$

[0092] Note that the limit on the integrals is from the center of thevortex, r=0, to the edge at r=R. If the vortex is not circular, then Ris a function of the angle, θ. When the swirl number is less than about0.4, the value of S can be estimated by$S = {{\frac{\gamma/2}{1 - \left( {\gamma/2} \right)^{2}}\quad {when}\quad \gamma} < 0.4}$and${S = {{\frac{\gamma/2}{1 - {\gamma/2}}\quad {when}\quad \gamma} > 0.4}},$

[0093] where γis the ratio of the maximum azimuthal to axial velocity.In this application, the value of S is between 0.01 for very weak swirlto 5.0 for very strong swirl in the flow, depending on the degree ofshear and turbulence desired in the flow field. For various grades ofpaper, for example, the value of swirl may be changed through this rangeas outlined below.

[0094] There are several mechanisms by which the RAPV can be generatedin a jet. The first is due to the hairpin vortex forming in the wake ofa protuberance in the jet, as shown in FIGS. 15 and 16. The protuberancein these figures is placed at the exit of the small diameter tube orafter the expansion in the larger diameter tube. As the flow approachesthe base of the protuberance, a streamwise velocity gradient formsresulting in a rolling flow towards the base of the protuberance.Depending on the shape of the protuberance, a standing vortex may or maynot exist at the upstream base. The rolling vortex then bends around theprotuberance and is swept upward with the flow forming a horseshoe-likevortex. The upward motion of the fluid splits the jet generating a CVPin the wake of the protuberance. This action can also be generated witha jet of a second fluid impinging at an angle on the primary jet fromthe small diameter tube or the flow inside the larger diameter tube asshown in FIGS. 17 and 18, respectively. The primary flow consists ofFluid A which is the fiber suspension. The second fluid, that is FluidB, is used for generation of the CVP in the mainstream throughinteraction with the primary flow. This interaction could either takeplace at the outlet of the smaller diameter tube or further downstreaminside the larger diameter tube.

[0095] Further enhancement of the tube design is to separate the outletregion of each tube into two sections such that each vortex in the CVPwill enter one subdivided tube. Then in FIGS. 11 to 14, there will be 18distinct outlet regions from 9 tubes in three rows and three columns.

[0096] It is important to note that the vortex patterns in FIGS. 11 to14 are generated with one protuberance inside the tube, and that twoprotuberances at 180° apart, will generate two pairs of CVPs, as shownin FIGS. 19 and 20; and . . . N protuberances at 360°/N apart willgenerate N CVPs. It is also possible to place the protuberances atunequal angular position.

[0097] The consequence and benefits of generating axial vorticity insideindividual tubes in the tube block of a headbox provides one or morecounter-rotating vortex pairs (CVP) inside each tube instead of just onevortex per tube. The counter-rotating vortices inside the tubes resultin more effective interaction of the jets once leaving the tubes.Depending on the application, the CVPs are generated in fourorientations in the tube block, as demonstrated in FIGS. 11 to 14, asdiscussed above.

[0098] In FIGS. 21-23, in order to achieve the largest level of swirl inthe small diameter tube 120, the spiral fins 122, 124, and 126 aredesigned to follow a spiral tubular section where all of the flow 128has to pass through one of the spiral tubular passages. This will guidemost of the flow 128 through the spiral section of the fins 122, 124,and 126, instead of the middle bore section. Since as shown in FIG. 23,most of the flow 128 follows the spiral streamline parallel to the finsurface, the swirl number will be increased. This is because the swirlnumber, as defined above, is proportional to the integral of the mass offluid times the angular to axial momentum ratio. The larger the mass offluid undergoing the swirl motion, the larger the swirl number. Moredetails on this system is provided below. The closed core 130 in thespiral section followed by the open core in the downstream sectionprovides a much higher swirl number in a smaller diameter tube.

[0099] With a wide diameter tube, e.g., greater than 27 millimetersinner diameter (ID), three (3) internal fins were found optimal whenused in the described embodiments, the wide diameter tube allowing foran open center without the fins extending to a solid central core. Ithas been observed that with such wide diameter tubes, i.e., greater thanapproximately 27 or 28 millimeters, the vortex strength is sufficientlylarge using the open core embodiment. In many paper machine headboxes,however, the ID is often limited to approximately only 20 millimeters,and thus as shown in FIGS. 21-23, the tube design utilizes a solidcenter core 130 upstream with a partially solid and partially open tubeembodiment to generate the sufficient amount of vortex strength desiredin the smaller diameter tube 120. This is much more difficult tofabricate and manufacture, and thus while the larger diameter tube ispreferred with the open core, often in the particular paper machineapplication, the parameters result in a limited diameter, i.e., lessthan 27 millimeters, in which to generate the same amount of vorticityin the smaller area.

[0100] With reference to FIGS. 24-30 discussed further below, thegeometry of mesh flow diagrams illustrates the axial velocity componentsof the vorticity generated with the described tube 120 embodiment ofFIGS. 21-23. Whereas the solid core 130 facilitates the sufficientvortex strength, it should be appreciated that the use of an open corein the small diameter tube, of a sufficient opening to avoid plugging ofthe tube, requires an opening such that the fluid flow 128 through thetube towards the center of the tube, without experiencing the rotatingeffects of the fins 122, 124, and 126. Thus, where the diameter of thetube is small, e.g., ID less than 27 millimeters, then to generate thesame strength vorticity as the large diameter open central core tube,the open area should be reduced greatly to generate the sufficientvelocity vortex, so most of the flow 128 would go between the fins 122,124, and 126 to experience the rotation. The problem however in practiceis that the use of a small open area cannot practically be sufficientlyreduced for a tip to tip distance between fins of less than 6 to 7millimeters due to the potential for fiber stapling which may occur,causing the tube 120 to plug.

[0101] As discussed, keeping the area in between the tip of the finsufficiently large with the small diameter tube 120 causes too muchfluid to tend to go straight through the center without experiencing therotating effects of the fins. Thus, the downstream effect of vorticitywould be very weak because most of the fluids would not have been forcedto rotate. With the center plugged, as shown in FIGS. 21-23, the solidcentral core 130 however requires that all of the flow 128 go along thefins 122, 124, and 126 and therefore the fluid is required to initiate arotational movement as it passes the core and enters the open areadownstream in the tube 120. Inside the tube, since the fluid is alreadyexperiencing a rotating effect, it tends to fill in between the fins asthe flow moves downstream, resulting in a centrifugal force which pushesoutwardly, facilitating its sufficiently large vortex strength.

[0102] Filling the entire region with a closed core however results in afluid downstream at the end of the fins having no velocity, thus thefins tend to collect fibers at the tip which creates fiber flocs.Advantageously, with the solid core design of FIGS. 21-23, where thepartial core is filled and the downstream half is open, a strongermixing force results in the core region, where the fins 122, 124, and126 are still operating. Therefore, any kind of fiber buildup isprevented at the zero velocity point at the down-stream end of the solidcore. The plots of FIGS. 24-30 show the effects for fluid flow 128 goingin between the fins in the two dimensional views, where the cross vectorvelocity plots in the cross-sectional plane illustrate the full strengthfacilitating the flow initially staying around the solid core in betweenthe fins and then mixing while a rotational flow is achieved downstreamwith the remaining fluid flow.

[0103] If the orientation of all of the fibers in a given surface areaof the sheet, for example in a square centimeter of the sheet, can bemeasured, and the number of fibers in each angular increment, forexample every 10 degrees, can be counted and plotted in a “fiberorientation polar plot”, then the level of fiber network anisotropy canbe evaluated. For example, in FIG. 31, the fiber orientation anisotropyis shown as an elliptical polar diagram with the major axis in themachine direction. The length of the line OA is proportional to thenumber of fibers oriented in the general direction of line OA.

[0104] In FIG. 31, the ratio of the major axis to the minor axis, thatis OB/OC, is referred to as the MD/CD fiber orientation ratio. The polardiagram is usually measured by measurement of the propagation of speedof sound in the ultrasonic frequency in a given direction in the planeof the sheet of paper. In a given direction, the speed of sound squaredis proportional to the elasticity of the sheet which in turn isproportional to the orientation of fibers in a given direction. Thesevalues are measured routinely by commercial instruments such as theLorentzen & Wettre (L&W) instrument.

[0105] The MD/CD fiber orientation ratio in conventional machines istypically greater than 1.2, and often substantially greater than thisratio indicative of anisotropic fiber orientation. Several examplesoutlined in Tables 1-4 below are provided with five samples in each testrun to provide an average MD/CD ratio determination for various headboxconfigurations. Table 1, indicating a control run, shows a substantialMD/CD ratio on average. For the tube bank configurations for Tables 2-4,headbox configurations have been identified for reducing the averageMD/CD ratio to obtain a ratio closer to 1.0. TABLE 1 MD/CD Test Resultsfor Tube Bank: CNTL6 (marked on sample and process as CRL6) Sile Open:1.25″. Cons. = 0.65% Process ID Sample Sample Sample Sample SampleAverage J/W ratio (head box) #1 #2 #3 #4 #5 (MD/CD) STDEV. (Water. P)CNTL6-1 2.07 2.04 2.20 1.92 2.21 2.088 0.411 0.947 CNTL6-2 1.58 1.631.70 1.63 1.52 1.612 0.067 0.981 CNTL6-3 1.35 2.32 1.37 1.54 1.40 1.5960.078 0.999 CNTL6-4 1.27 1.33 1.19 1.17 1.14 1.220 0.121 1.037 CNTL6-51.74 1.74 1.67 1.67 1.73 1.710 0.037 1.078

[0106] TABLE 2 MD/CD Test Results for Tube Bank: R406 Sile Open: 1.25″.Cons. = 0.65% Process ID Sample Sample Sample Sample Sample Average J/Wratio (head box) #1 #2 #3 #4 #5 (MD/CD) STDEV. (Water. P) R40-6-1 1.251.28 1.36 1.39 1.32 1.320 0.057 0.985 R40-6-2 1.28 1.34 1.23 1.28 1.241.274 0.043 0.993 R40-6-3 0.97 0.89 0.97 0.94 0.89 0.932 0.040 1.015R40-6-4 0.96 0.97 0.87 0.98 0.91 0.938 0.047 1.035 R40-6-5 0.98 1.071.07 1.00 0.98 1.020 0.046 1.056 R40-6-6 1.36 1.48 1.49 1.50 1.44 1.4540.057 1.083 R40-6-7 1.66 1.55 1.64 1.66 1.68 1.638 0.051 1.103

[0107] TABLE 3 MD/CD Test Results for Tube Bank: R40-6GK Sile Open:1.25″. Cons. = 0.65% Process ID Sample Sample Sample Sample SampleAverage J/W ratio (headbox) #1 #2 #3 #4 #5 (MD/CD) STDEV. (Water. P)R40-6GK-1 1.63 1.52 1.52 1.61 1.65 1.586 0.062 0.978 R40-6GK-2 1.52 1.401.35 1.41 1.34 1.404 0.072 0.996 R40-6GK-3 1.10 1.06 1.02 1.09 0.961.046 0.057 1.016 R40-6GK-4 1.03 0.96 0.94 0.97 0.98 0.976 0.034 1.041R40-6GK-5 1.39 1.41 1.30 1.25 1.39 1.348 0.069 1.062 R40-6GK-6 1.60 1.491.53 1.59 1.58 1.558 0.047 1.081 R40-6GK-7 1.69 1.73 1.71 1.69 1.701.704 0.017 1.101

[0108] TABLE 4 MD/CD Test Results for Tube Bank: R40-6SR Sile Open:1.25″. Cons. = 0.65% Process ID Sample Sample Sample Sample SampleAverage J/W ratio (headbox) #1 #2 #3 #4 #5 (MD/CD) STDEV. (Water. P)R40-6SR-1 1.71 1.54 1.49 1.59 1.66 1.598 0.089 0.985 R40-6SR-2 1.31 1.281.24 1.37 1.50 1.340 0.101 1.005 R40-6SR-3 0.98 1.08 0.86 0.98 0.880.956 0.089 1.027 R40-6SR-4 0.94 0.98 0.86 1.02 0.90 0.940 0.063 1.045R40-6SR-5 1.07 1.10 0.97 1.31 1.31 1.152 0.152 1.057 R40-6SR-6 1.29 1.421.56 1.39 1.72 1.476 0.167 1.082 R40-6SR-7 1.70 1.72 1.74 1.67 1.611.688 0.051 1.098

[0109] With reference to the data indicated above, and in view of theobserved elastic content identified in FIG. 34, substantialreorientation of fibers in the web product may be achieved. FIG. 34provides a polar diagram of the in-plane ultrasonic velocity squared, toindicate the elastic content showing the orientation distribution of thestrength of the fiber-board sheet The sample is provided from the pilottrials produced using 26 pound linerboard with the described system. Thepolar plot of the fiber orientation illustrates the ability to turn theaxis of the fiber content being produced in the web product more towardsthe CD direction with less fibers being oriented in the MD direction.This provides for the strength in the CD direction as being as large asthe strength in the MD direction. Accordingly, the specification ofpaper manufacture for packaging and other paper products with respect tothe CD machine direction strength may be achieved with less fibercontent. Once the strength in the CD direction is increased, theproduction process may be optimized for predetermined weight per squaremeter of sheet of paper or a certain amount of fiber content to meetminimum CD strength specifications. Of course, the strength in the MDdirection will be lower because of the reorientation of fibers,providing less fibers oriented in the MD direction, however the MDdirection usually has substantially more strength than the CD directionin conventional paperboard manufacture.

[0110] The axial velocity at different angles downstream is shown ascross sections at the plotted angles, for example, the 22 millimeterdiameter tube embodiment illustrates axial velocity at zero, 30, 60, 90,120, and 150 degrees (180 being the same as zero degrees). As shown,from only 5 millimeters to one diameter (22 millimeters) passed the endof the tubular region, the flow from the straight section is illustratedin which the velocity field quickly becomes uniform. Looking at thestream line velocity component at different cross sections, at theindicated angles, shows the flow going between the fins at a highervelocity than the flow moving along the fins. Thus, the flow around themiddle of the fin is at a somewhat higher velocity than the flow nearthe edge of the fin which is slower but which flow very quicklyequilibrates with the remaining fluid flow. With the plot showing 45degrees at half the fin and one diameter across the fin, the flow isalso shown as very quickly becoming more uniform, i.e., the x and ycomponents of the swirling velocity. Accordingly, the tube 120 design ofFIGS. 21-23, and the mesh flow diagrams of FIGS. 21-30, illustrate afurther approach for enhancing swirl in smaller diameter tubes of thedescribed system with one to two diameters of downstream straightsection flow from the tube resulting in the flow achieving a uniformvelocity in the nozzle of the headbox.

EXAMPLES

[0111] With reference to FIGS. 24-30, these plots and figures are frommodel D27 which was built in finite element mesh generation program andrun using finite element analysis to simulate the above approach. Thegeometry is as follows: Tube diameter:  22 mm Center diameter:  6 mmPitch:  40 mm Rotation: 360 degrees Number of fins:  3 Fin geometry:Tapered from 3 mm thickness at the base to 1.5 mm at the tip which isrounded. Center geometry: The center core region is filled with atorpedo shaped block which runs from 3 mm before the start of the finsto 2 mm into the fin section. Before the start of the fins, the block ishemi- spherical. From the start of the fins to 10 mm back, it is astraight circular cylinder. From 10 mm until it ends at 20 mm, it tapersas a cone with a rounded tip. The fins meet the center block at a rightangle and with rounds from 0 to 10 mm. At 10 mm, as the block tapers,the fins leave the block and the tips blend quickly from flat to fullyrounded.

[0112] In the package are twelve plots. These are black and white lineplots chosen to reproduce well and be clear at small sizes. In keepingwith this, they have minimal labeling.

[0113] The first three are engineering design program plots of thegeometry of the section containing the fins and center body as describedabove. (1) shows side and end views, (2) shows only the side view, and(3) shows only the end view. The flow characteristics illustrated,rather than the dimensions (not shown), in FIGS. 23-30 will be readilyappreciated by those skilled in the art.

[0114] These drawings are followed by a series of nine plots presentingtypical results from finite element analysis.

[0115] The model was generated in finite element mesh generation programto represent a simplified version of the true geometry. The leading andtrailing edge rounds were deleted from the fins and all surfaceintersections were taken to be sharp. An upstream section of straightcircular duct was added with flow entering as a jet of 9 mm diameter andquadratic profile 60 mm upstream of the fins. A straight circular ductof 150 mm length was added to the outlet. The volume was meshed withlinear brick elements and all external surfaces were meshed with lineartetrahedral elements. The final model contains 361,200 elements with344,830 nodes.

[0116] This model was run simulating water at 40° C. and with a flowrate of 20 gpm. The computational velocity was scaled such that one“unit” of velocity in finite element analysis corresponds to 4 mm/s inreality. This was done to aid convergence. Other properties wereadjusted to keep the Reynolds number consistent The model was set forincompressible, steady, turbulent flow, and used the standard k-epsilonformulation as included in finite element analysis. The inlet boundarycondition was given by the flow rate and includes a small inletcomponent of kinetic energy and dissipation to “kick start” thek-epsilon routine. Wall boundary conditions are the no-slip andimpermeability conditions, and, additionally, the wall imposes a Law ofthe Wall formulation on all volume elements directly touching the wall.The outlet has a free boundary condition. There is a Stokes initialcondition applied through the volume for velocity and a uniform lowvalue of kinetic energy and dissipation, again to “kick start” thek-epsilon routine. The simulation converged in 251 iterations and used279,022 processor seconds (approximately 3.2 days).

[0117] The swirl number for this case was calculated by integrating theswirl number along a series of radii 30 degrees apart. It was calculatedat 5 mm and one diameter past the fins. The results are given below: At5 mm: 0.3156 At 1 dia: 0.2786

[0118]FIG. 31 is a polar diagram illustrating the anisotropic fiberorientation illustrates fiber orientation with a preference to themachine direction;

[0119]FIG. 32 illustrates the reorientation of paper fibers providingisotropic fiber orientation for discharge as a web product resulting inhigher cross-machine direction (CD) strength providing fiber orientationsubstantially equally in all in-plane directions as shown in the polardiagram; and

[0120] FIGS. 33A-33C illustrate various manifestations of fiberorientation nonuniformity showing anisotropic paper having preferentialfiber orientation which is typically distributed relative to the machinedirection as shown in the polar plots, whereas FIG. 33D illustrates auniform isotropic orientation.

[0121] With reference to FIGS. 31 and 32, whereas the ratio of the majoraxis to the minor axis in FIG. 31 illustrates anisotropic fiberorientation with a preference to the machine direction, FIG. 32 shows anisotropic fiber orientation which is achieved when the paper fibers areoriented approximately equally in all in-plane directions resulting inthe circular polar diagram of FIG. 32. It will be appreciated that theisotropic fiber orientation results in higher cross-machine (CD)strength as indicated from the dashed line polar plot outline in FIG. 32extending in the solid circular polar diagram in the CD direction. Theadditional CD strength accordingly results in the ability to manufacturea paperboard product having lighter weight sheets with the same CDperformance, additional use of recycled fiber product, improved printingsurface and superior dimensional stability. Additionally, the processresults in a system requiring less energy consumption and thus fiberconception while providing increased productivity advantages. Asdiscussed further in connection with the examples set forth below,increased CD strength of approximately 7-25% in CD specific STFIlinerboard strength results in reduced basis-weight for the same levelof sheet performance. Additionally, common problems such as twist, warp,and sheet curl, and the dependence upon jet wire speed, aresubstantially alleviated. Thus, decoupling of formation and fiberorientation allows more flexibility in headbox design to achieve betterformation. The grades of paper product most significantly impactedinclude linerboard and corrugated medium, bleached board, kraft paper,coating paper and board, and tissue products. For example, it may beanticipated that a 10% increase in CD strength may result inapproximately 9% less fiber requirement for meeting the specification ofstrength and quality. It may be appreciated therefore that the reducedfiber requirement results in energy costs per ton of product which issubstantially reduced. The headbox tube design may advantageously beprovided as a retrofit to existing tube sections of current headboxeswhich maybe provided as a simple retrofit requiring a minimal amount ofmachine downtime.

[0122] It will be appreciated by those skilled in the art thatmodifications to the foregoing preferred embodiments may be made invarious aspects. The present invention is set forth with particularityin the appended claims. It is deemed that the spirit and scope of thatinvention encompasses such modifications and alterations to thepreferred embodiment as would be apparent to one of ordinary skill inthe art and familiar with the teachings of the present application.

What is claimed is:
 1. A paper forming machine headbox component forreceiving a paper fiber stock and generating a jet therefrom fordischarge upon a wire component moving in a machine direction (MD), theheadbox component comprising: a distributer for distributing stockflowing into the headbox component in a cross-machine direction (CD),the distributer effective for supplying a flow of said stock across thewidth of the headbox in the machine direction; a nozzle chamber havingan upper surface and a lower surface converging to form a rectangularoutlet lip defining a slice opening for the jet; a diffuser blockcoupling said distributer to said nozzle chamber, said diffuser blockcomprising a multiplicity of tubular elements disposed between saiddistributer and said nozzle chamber, said tubular elements beingoriented axially in the machine direction, a plurality of the tubularelements having a longitudinal axes in the direction of the flow ofstock, and the tubular elements arranged within the diffuser block as amatrix of rows and columns for generating multiple jets of said stockflowing into said nozzle chamber; and said tubular elements beingoriented axially generate an axial vorticity which prevents fiberorientation in the machine direction in an initial converging section ofsaid nozzle chamber being effective for swirling said stock incontrolled pairs of axial vortices along the longitudinal axes of thetubular elements as said stock flows through said tubular elementspromoting mixing of the jets of said stock as said jets flow into saidnozzle chamber from the tubular elements to form a uniform flow of stockat the slice opening for the jet.
 2. A headbox component as recited inclaim 1 wherein said diffuser block orienting said tubular elementsaxially in the machine direction generates machine direction strain andacceleration in said nozzle chamber with a gradual convergence rate nearthe slice which is not strong enough to orient the fibers in the machinedirection.
 3. A headbox component as recited in claim 2 wherein thefibers in the forming jet will be isotropic, uniformly oriented in alldirections.
 4. A headbox component as recited in claim 1 wherein saidtubular elements comprise a closed core with a spiral section followedby the open core in the downstream section for enhanced swirl in a smalldiameter tube.
 5. A paper forming method for receiving a paper fiberstock and generating a jet from a headbox component for discharge upon awire component moving in a machine direction (MD), the methodcomprising: distributing stock flowing into the headbox component in across-machine direction (CD), to a distributer effective for supplying aflow of the stock across the width of the headbox in the machinedirection; converging the flow of the stock with a nozzle chamber havingan upper surface and a lower surface to form a rectangular outlet lipdefining a slice opening for the jet; coupling the distributer to adiffuser block and nozzle chamber having a multiplicity of tubularelements being disposed and oriented axially therebetween in the machinedirection with longitudinal axes in the direction of the flow of stock,the tubular elements being arranged within the diffuser block as amatrix of rows and columns for generating multiple jets of the stockflowing into the nozzle chamber; and generating controlled axialvortices along the longitudinal axes of the tubular elements as thestock flows through said tubular elements promoting mixing of the jetsof the stock as the jets flow into the nozzle chamber from the tubularelements to form a uniform flow of stock at the slice opening.
 6. Amethod as recited in claim 5 wherein the tubular elements are orientedaxially to generate an axial vorticity which prevents fiber orientationin the machine direction in an initial converging section of the nozzlechamber.
 7. A method as recited in claim 5 wherein the tubular elementsare oriented axially in the machine direction to generate machinedirection strain and acceleration in the nozzle chamber with a gradualconvergence rate near the slice which is not strong enough to orient thefibers in the machine direction.
 8. A method as recited in claim 7wherein the generating step isotropically orients the fibers in theforming jet in all directions.
 9. A web product being formed from paperfiber stock, comprising: generating a jet from a headbox component fordischarge upon a wire component moving in a machine direction (MD);distributing the paper fiber stock into the headbox component in across-machine direction (CD); converging the flow of paper fiber stockin a nozzle chamber; coupling a diffuser block between the distributorand the nozzle chamber to provide a multiplicity of tubular elementsbeing disposed and oriented axially therebetween in the machinedirection with longitudinal axes in the direction of flow of the paperfiber stock for generating multiple jets of stock flowing into thenozzle chamber; and generating controlled axial vortices along thelongitudinal axes of the tubular elements as the paper fiber stock flowstherethrough to form a uniform flow of stock at the slice opening toprovide isotropic fiber orientation in the web product.
 10. A webproduct as recited in claim 9, wherein the process for producing the webproduct comprises generating machine direction strain and accelerationin the nozzle chamber with a gradual convergence rate near the slice.11. A web product as recited in claim 9, comprising providing a closedcore with a spiral section within the tubular elements followed by anopen core in the downstream section.
 12. A web product as recited inclaim 9, wherein the tubular elements generate controlled axial vorticesas the paper fiber stock flows therethrough.
 13. A web product asrecited in claim 9, wherein the MD/CD fiber orientation ratio isapproximately unity indicating fibers being substantially uniformlyoriented in all directions in the web product.
 14. A web product asrecited in claim 9, wherein the elastic content of the web productindicates orientation distribution of strength in the web product asbeing substantially uniform from the MD to the CD directions.